A number of arrangements for indexed rotation are known in the prior art. Many disclosures are related to lathes, or revolving tables for machining.
A. R. Brualt's U.S. Pat. No. 3,380,322 Apr. 30, 1968 describes a technique for rapidly and accurately setting angular indexed work. Angles are set with aid of a fixed index. It is necessary to set indexing sliding member 12. It is not continually variable and is not automatically indexed.
Alan Pearson and U.S. Pat. No. 2,524,538 Oct. 3, 1950 describes an indexing device utilizing many pins circumferentially placed about a work table. Arc positioning is only referenced to one pin at a time. Only small angles of an arc are measured.
W. Shotey's U.S. Pat. No. 3,088,340 May 7, 1963 and E. S. Firestone et. al. U.S. Pat. No. 3,177,740 Apr. 13, 1965 feature ball bearing indexing. This technique allows for definitive placement but relies on conventional scales for measuring arc and is not continuously variable.
H. M. Minnis' U.S. Pat. No. 617,689 Jan. 10, 1899 relies on an array of clocks with different time designations. This arrangement measures activity with cyclical passage of time. It does not relate to movement but only scheduling.
The adjustment knob of W. H. Vogt's U.S. Pat. No. 2,220,590 Nov. 5, 1940 reveals degree of rotation about a fixed index. It is not continually variable.
The Meditimer of Villa-Real's U.S. Pat. No. 4,345,541 Aug. 24, 1982 relies on setting the last dose time. Simultaneously, another set point reveals the next dosage time. The user rotates an index between two set fixed points.
The above inventors are not dealing with the problem of beginning a measurement of rotation at any possible random point. Monitoring the tightness of an oil filter is a specific application. A guide is needed to assure confidence of the operator.